To get on to the question. Quite a common thing is that on the ACB the light comes on indicating that power is going to a pump but the voltage is not full 230v.
Once it gets less than about 170v the affected pump slows or fails to work completely.
This is due to an often heat sensitive fault on the octocoupler chip immediately to the right of the relevant light.
Basically these things are the modern equivalent of a relay.
Sometimes the situation will improve if you leave the cover off.
When the pump light is on applying heat with a hair dryer and then cooling the chip down with an air duster has proved a faulty octocoupler by checking the output voltage.
Quite often there is a spare chip at the top that you can see on page 22 of
these instructions which could possibly be moved down to the location of the faulty one or as I got away with once rerouting the wire on the board so that this spare chip was used and simply followed the track to pick up a new switched live location
It cost me about £35 to get 10 of these chips from China through ebay but I would probably need a 'heat station' to remove and replace one. Better than a soldering iron these spread a flow of very hot air across the area at the back of the chip allowing the full chip to be removed in one piece. One day when I'm not so busy I will get all my old boards together and give them to a mate who can sort a few out for me.
When going through the sensor test sequence and you get to the 'H' give the wire a wiggle near the sensor to see if the 'er appears after it. [Hºer] Sometimes this denotes an intermittent fault.